Research interests: Given that seasonal biomass burning is widespread in Sub-Saharan Africa, can the effects of this burning on the environment be measured regionally and globally? This is one of the questions NASA scientist Dr. Charles Ichoku seeks to answer in his research examining the effects of wildfires, agricultural burning, and the emissions associated with these activities. Through a variety of measurement and modeling approaches coordinated under an interdisciplinary framework, Dr. Ichoku is helping scientists, researchers, and natural resource managers gain a better understanding of environmental change and climate variability in Northern Sub-Saharan Africa (NSSA) caused by seasonal fires and how these changes may impact the water cycle and other processes not just in this diverse region, but around the world.

Current research focus: The NSSA region straddles the African continent from east to west, and is bounded on the north by the Sahara Desert and on the south by the equator. While the northern edge of this vast region is dry and sparsely populated, seasonal moisture becomes more abundant towards the equator. As the summer rains taper off and the dry season begins around November, wildfires and agricultural burning become common. Peak biomass burning generally occurs November through January, then tapers off in March and becomes virtually non-existent in the summer. These fires, most of which are human-set, are used to clear land for cultivation or other agricultural purposes as well as to help increase soil nutrients. This burning also contributes high quantities of fine particles, called aerosols, into the atmosphere. In fact, the NSSA region is estimated to contribute 20-25% of the global annual carbon emissions from open biomass burning. This seasonal burning not only impacts landcover, it also affects parts of the energy and water cycles and, through these, potentially also rainfall patterns.

Dr. Ichoku and his colleagues are exploring the effects of this seasonal biomass burning on land-cover and ecosystem changes, surface albedo, smoke and dust emissions, atmospheric heating rates, and how these factors in turn affect the difference between the amount of sunlight absorbed by this region and the amount reflected back into space. As part of this research, they developed a model of the NSSA regional climate system components that may be affected by biomass burning, and analyzed a variety of satellite data covering the years 2001 to 2014 along with relevant model-simulated data and data collected from field investigations.

Through the use of this interdisciplinary approach, the research team is conducting a comprehensive study of Sub-Saharan African biomass burning to understand and clarify the impacts of this on the region’s water cycle. The team seeks to determine how the fire-induced surface and atmospheric changes affect rainfall variability, soil moisture content and retention, surface runoff, infiltration, and groundwater mass balance, particularly in the Lake Chad Basin and surrounding regions. The Lake Chad Basin alone covers an area of about 2,335,000 sq. km (902,000 sq. mi) across parts of seven countries in north central Africa, and is home to more than 30 million people.

Data products used:

The Moderate Resolution Imaging Spectroradiometer (MODIS) Land Cover Type product (MCD12Q1), which provides data characterizing five global land cover classification systems. These data are available through the Land Processes Distributed Active Archive Center (LP DAAC).

Surface evapotranspiration data from the Global Land Data Assimilation System Version 1 (GLDAS-1) Noah Land Surface Model monthly data set at 0.25˚x0.25˚ spatial resolution.

Research findings: Using more than 10 years of MODIS fire and albedo data products, Dr. Ichoku and his colleagues were able to assess the areas burned throughout the NSSA region and the times these areas burned. The team found that the spatial-temporal extent of fires in Sub-Saharan Africa is widespread, and the disturbance rates from year to year remain fairly steady. The team determined that biomass burning in the NSSA produces a net decrease in surface albedo, meaning that the burned areas do not reflect as much incoming solar radiation, and that these albedo changes vary with the type of vegetation burned (woody savanna/savanna, evergreen broadleaf, cropland, etc.). The results of this research are useful in determining the effects of albedo changes caused by biomass burning on soil moisture budget, evapotranspiration, infiltration, and runoff, all of which affect the water cycle. In addition, the team’s research indicates that humid West Africa shows an increasing trend of April biomass burning and that this increase in burning seems to delay the onset of daytime warm rain processes, which further impacts the region’s water cycle.

Dr. Ichoku also determined that global fire emissions from biomass burning can be assessed through the use of remotely-sensed satellite data, such as the NASA MODIS aerosol and fire products. These research findings will help improve the estimation of emissions of various smoke constituents and their contributions to atmospheric aerosol concentrations.